Process for cooling during regeneration of fluid cracking catalyst

ABSTRACT

In a process apparatus for the regeneration of fluid cracking catalyst, the catalyst is cooled in an exchanger mounted to the lower side of the regenerator and cool catalyst is returned to the regenerator by means of gas lift.

CROSS REFERENCES TO RELATED APPLICATIONS

U.S. Ser. No. 532,253 filed Sept. 15, 1983; refiled Sept. 17, 1984 asU.S. Ser. No. 617,764; U.S. Ser. No. 688,469 filed Jan. 3, 1985 U.S.Ser. No. 617,764 filed June 6, 1984 and U.S. Ser. No. 355,661 filed Mar.12, 1982 relate to the general field of the present invention.

BACKGROUND

(1) Field of the Invention

This invention relates to the field of hydrocarbon conversion with fluidcatalytic cracking catalyst. In particular, it relates to theregeneration of coked catalyst by conversion of coke on catalyst withcontrol of the temperature of regeneration.

(2) Description of the Prior Art

The FCC process converts petroleum feedstocks boiling in the gas oilboiling range to lighter products such as gasoline. To obtain maximumconversion efficiency from the very active zeolite cracking catalyst, itis necessary to remove as much coke as possible during the regenerationstep of the FCC process. Accordingly, modern regenerators are operatedin the high temperature regeneration mode. Regeneration temperatures inthe range of to 538° C. to 787° C. (1000° F. to 1450° F.), morepreferably 621° C. to 732° C. (1150° F. to 1350° F.) and most preferably677° C. (1250° F.) to 732° C. (1350° F.) are employed.

Increasingly, catalytic cracking units are being adapted to theconversion of feedstocks heavier than gas oil. Such carbo-metallichydrocarbon oils contain relatively large amounts of coke precursors,e.g. asphaltenes and heavy aromatic hydrocarbons. In addition,carbo-metallic cracking feedstocks contain complex organo-metalliccompounds which deposit on the cracking catalyst as it circulatesbetween the cracking zone and the regeneration zone. The most difficultproblem encountered in the conversion of carbo-metallic oils is the hightemperatures which can occur during the burning of carbon from the fluidcatalyst particles. Since the hi-tech zeolite cracking catalyst byprolonged exposure to temperatures above about 704° C. (1300° F.) to815° C. (1500° F.) is known to deteriate, it is essential that theregeneration procedure be carefully controlled.

Various types of catalyst coolers are presently applied to regeneratorsand most of these coolers are based on indirect heat exchange employingtubular heat exchangers located inside or outside of the regenerator.Prior art FCC regenerators with coolers are disclosed in U.S. Pat. Nos.2,377,935; 2,386,491; 2,662,050; 2,492,948; and 4,374,750.

The regenerator of the present invention is particularly applicable tocontrol of catalyst cooling in situations where the catalytic crackingunit is revamped to convert feedstocks heavier than gas oil on a full orpart-time basis. Two such cracking units are shown in HydrocarbonProcessing September, 1962, page 156 and Hydrocarbon Processing,September, 1970, page 177.

In addition, the process and apparatus of the present invention can beused in the regeneration of coked non-catalytic fluid solids like thoseused for decarbonization and demetallization of carbo-metallicfeedstocks. One such process is disclosed in U.S. Pat. Nos.: 4,469,588to Hettinger et al (Ashland Oil, Inc.) 4,434,044 to Busch et al (AshlandOil, Inc.) and 4,414,098 to Zandona et al (Ashland Oil, Inc.)

SUMMARY OF THE INVENTION

The present invention provides an economical means of adding a catalystcooler to the regenerator of a fluid catalytic cracking unit. A heatexchanger is mounted on the bottom section of the regeneration vesseland following the cooling step the catalyst is returned to theregenerator by means of a gas lift device. The process and apparatus ofthe invention can be employed on an existing FCC in situations where itis desired to go from partial carbon monoxide burn to fall CO burn andadditional heat removal capacity is required to control regeneratortemperature.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a sectional elevation of a regeneration apparatusaccording to the invention showing single stage regeneration, a downflowcooler and a gas lift device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention comprises a process and apparatus for theregeneration of coke contaminated fluid cracking catalyst wherein cokeis burned from the catalyst in the dense bed of the regeneration zonewhile some catalyst is being continuously removed to and through adownflow cooler with continuous return of the cooled catalyst byvertical gas lift to the desired location in the dense bed.

The FCC feedstock, which results in a carbon-on-catalyst beforeregeneration above about 1%, can be desalted whole petroleum crude oil,atmospheric gas oil, vacuum gas oil, carbo-metallic fractions fromvarious pretreating steps such as hydrodesulfurization, demetallationand solvent extraction, coker gas oil, visbroken stocks, recyclefractions and blends of the foregoing materials.

The fluid cracking catalyst used for cracking and requiring continuousregeneration may be of the conventional type such as activated clay,silica alumina, silica zirconia, etc. But natural and synthetic zeolitetype catalysts comprising molecular sieves in a matrix having an averageparticles size ranging from about 30 to about 100 microns are preferred.

Following the cracking, disengaging and stripping steps, the catalyst ispassed to the regenerator with a carbon burden of about 0.75 to 1.5 wt%carbon on catalyst. To maintain the cracking efficiency and theselectivity of the catalyst to gasoline and light hydrocarbon products,the carbon on catalyst should be reduced to less than about 0.1wt%during regeneration.

One advantage of the present invention is that it provides aninexpensive apparatus (cooler) and process to control regeneratortemperature without resorting to multi-stage regeneration. Anotheradvantage of the invention is that continuous control of the coolingoperation is maintained.

Referring now to the drawing, reference numeral 1 denotes theregenerator of a fluid catalytic cracking unit. Coked catalyst isstripped in a stripping unit, not shown, and passed via line 2 into theregenerator at a suitable level of the catalyst bed 3. Oxygen containingregeneration gas is passed by line 4 to air grid 5. Continuouscombustion takes place in the catalyst bed as the regeneration gas (air)and the coke on the catalyst burn to form spent regeneration gascomprising CO₂ and CO and other gases. The ratio of CO to CO₂ depends onthe amount of CO burning desired or required.

Spent regeneration gas is passed thru cyclones, not shown, andrecovered.

Hot catalyst at a temperature of 621° C. to 815° C. (1150° F. to 1500°F.), preferably 649° C. to 760° C. (1200° F. to 1400° F.) is drawn fromthe bed of catalyst undergoing regeneration by line 6 under the controlof valve 7. The catalyst migrates downwardly through cooler 8 inindirect contact with cooling fluid circulating through a tube bundle,not shown. In a preferred embodiment, coolant is supplied and removed atthe bottom of the cooler. Water is supplied by line 9 and steam isremoved by line 10. Fluidizing gas can be supplied by line 11.

As it passes through the cooler, the temperature of the catalyst isreduced by about 66° C. to 121° C. (about 150° F. to 250° F.). Cooledcatalyst passes downwardly via line 12 to wye junction (Y shaped part)13. The flow of catalyst is then turned in the apex of the wye to movevertically upward through lift line 14 to regenerator bed 3. Lift line14 terminates in the dense bed above the air grid.

The flow of cooled catalyst is maintained by injecting a lift gas fromline 15 through control valve 16 and through nozzle 17. The lift gas inline 15 is separate from the regeneration gas in line 4. The nozzle isplaced at or near the center of line 14. The tip of the nozzle islocated in wye 13. The nozzle can be any device which constricts gasflow and orients an accelerated flow of gas vertically up through thelift gas tube. The cooled fluidized catalyst is lifted to a desiredlevel above air ring 5 and exits into the dense bed through port 18. Ithas been found that the cooled catalyst provides the best moderatingeffect when it is drawn from the dense bed and returned to the densebed. Regenerated catalyst is removed from the regenerator by line 20 forpassage to the cracking zone, not shown.

EXAMPLE

In a fluid catalytic cracking unit processing from about 750 to about1,000 barrels (BBL) of petroleum feed per hour, the coked catalyst isregenerated in a single stage regenerator. The dense bed of theregenerator has an inventory of 50 tons of catalyst.

It is necessary to provide catalyst to the cracking stage at atemperature in the range of 677° C. to 746° C. (1250° F. to 1375° F.).It is also necessary to control regeneration temperature below 815° C.(1500° F.) to prevent damage to the catalyst.

Accordingly, 0 to 15 tons per minute of hot catalyst is passed to cooler8. The catalyst is cooled to a temperature in the range of 593° C. to649° C. (1100° F. to 1200° F.) in the cooler.

Lift gas provided at a rate of 4700 SCFM lifts the catalyst through line14 to dense bed 3. Catalyst velocity is preferably 10 to 40, morepreferably 15 to 30, feet per second.

The present apparatus provides a means of adding a cooling component toan existing regenerator vessel. Catalyst is cooled by gravity passagethrough a downflow catalyst cooler, cool catalyst passes by gravity flowto a wye and a lift gas-nozzle combination is employed to return cooledcatalysts to the regenerator. The cooling system requires a minimalamount of space and a small quantity of piping, valves and controls. Theaddition of catalyst cooling enables the operator to use heavierfeedstocks which will deposit more carbon on the fluid crackingcatalyst. The additional heat release in the regenerator is compensatedfor by the cooler. The cooling process disclosed herein is controlled bya first valve which varies and controls flow of hot catalyst from theregenerator and second valve which varies and controls flow of coolcatalyst into the regenerator. Thus positive flow control is maintainedover the cooling system.

Specific compositions, methods, or embodiments discussed are intended tobe only illustrative of the invention disclosed by this specification.Variation on these compositions, methods, or embodiments are readilyapparent to a person of skill in the art based upon the teachings ofthis specification and are therefore intended to be included as part ofthe inventions disclosed herein.

Patents and literature referred to in the specification are expresslyincorporated herein by reference including patents or other literaturecited within them.

What is claimed is:
 1. A process for regeneration of coke contaminatedfluid cracking catalyst comprising in combination the steps of:A.maintaining a dense fluid bed of hot catalyst in a regeneration zone ata temperature in the range of 649° C. to 787° C. (1200° F. to 1450° F.),providing an oxygen containing regeneration gas injection point withinsaid dense fluid bed and passing coke contaminated catalyst into saiddense fluid bed at a point above the said regeneration gas injectionpoint; B. withdrawing a controlled stream of said catalyst from saiddense fluid bed at a point above said regeneration gas injection pointand passing said stream through a downflow indirect heat exchange zoneto cool said catalyst; C. passing cooled catalyst now at a temperaturein the range of 593° C. to 704° C. (1100° F. to 1300° F.) to the bottomof a gas lift zone located in approximately the same horizontal plane assaid heat exchange zone; D. passing the cooled catalyst by verticalaccelerated gas drive upwardly through the gas lift zone at a velocityof 15 to 30 feet per second by employing a lift gas separate fromregeneration gas; and E. lifting a controlled quantity of cooledcatalyst up into the dense bed of hot catalyst in said regenerationzone, above the said regeneration gas injection point whereby hotcatalyst is cooled by mixing with the cooled catalyst.
 2. A processaccording to claim 1 wherein said air injection point comprises an airgrid.
 3. A process according to claim 1 wherein said air injection pointcomprises an air ring.
 4. A process according to claim 1 wherein coolantis supplied and removed at the bottom of said downflow indirect heatexchange zone.
 5. A process according to claim 1 wherein water issupplied cool said indirect heat exchange zone.
 6. A process accordingto claim 1 wherein fluidized gas is additionally supplied to saidindirect heat exchange zone.
 7. A process according to claim 1 whereinindirect heat exchange zone communicates with the bottom of said gaslift zone through a function into which lift gas is injected.